1. Field of the Disclosure
Embodiments of the disclosure relates to a reflective display device, and more particularly, to a display device comprising color enhancers.
2. Discussion of the Related Art
A reflective display is a display device that displays information by using external light without a light source. An electrophoretic display, which is the most common reflective display, is a display device that induces electrophoresis of charged particles dispersed in a nonpolar solvent on a display surface under the action of an electrical field and displays an image using the optical properties of the solvent and the particles. The above electrophoresis display (EPD) has a lower power consumption than other flat panel displays (FPDs) and can keep displaying without power supply. Electronic paper, one of the most common implementation of an electrophoretic display, is drawing attention.
In general, electrophoretic displays are commonly classified into a microcapsule type electrophoretic display from E-Ink Corporation, which has microcapsules of charged particles thinly arranged and implanted into a dispersion solvent, and a microcup type electrophoretic display from Sipix, which has particles implanted into each of cups made in a microsize. In the microcapsule type electrophoretic display, encapsulated charge carriers are dispersed in a solvent filled with a specific dispersion solvent. As the microcapsules are charged by an electrical field, black and white are displayed on the opposing display electrodes. Also, color filters, a fluid colored with a dye or pigment, or colored electrophoretic particles are used to represent colors on upper edges of the display device, thereby implementing the electrophoretic display.
Meanwhile, an electrowetting apparatus disclosed in Korean Laid-Open Patent No. 2012-0021075 relates to a display device which displays different colors in such a way that a hydrophobic insulating material is laminated on an electrode, a voltage is applied to the water and the electrode when water and oil come in contact and causes the water contact angle to be decreased as the hydrophobic interface of the water becomes hydrophilic, and light is reflected from the reflecting electrode when the oil is pushed toward the pixel walls as the water contact angle is decreased. Accordingly, colors are represented by dispersing or dissolving a dye or pigment in an aqueous solution within color filters or cells.
Korean Laid-Open Patent No. 2010-0020105 discloses a technology, which represents black and other colors by using electrochromic elements as color filters for an electrophoretic display containing black and white particles. The color filters disclosed in this technology represent colors as red, green, and blue electrochromic materials are applied to each pixel by using electrochromism, which is displayed by some materials that change their color due to an oxidation and reduction when a voltage is applied.
A colored electrphoretic display is implemented in such a way that color filters are positioned on an upper plate to give a color to reflected light. Other implementations include driving electrophoretic particles in a colored fluid and driving colored electrophoretic particles in a transparent fluid. The colored electrophoretic display using color filters involves additional materials and additional process costs for the color filters to represent colors, which becomes a primary factor in the rise in unit cost, and also is not desirable in terms of the brightness and sharpness of colors basically due to light absorbed into a color filter layer when displaying colors. Moreover, the use of a colored fluid is not desirable because most of light is reflected from the upper edge of the colored fluid. In addition, the method of driving colored electrophoretic particles is disadvantageous in that the reflectance and color of light are determined by white particles that reflect the light.
U.S. Pat. Nos. 6,017,584 and 7,012,735 propose a display device using electrophoresis in which dual-colored electrophoretic particles charged with black and color are encapsulated. However, it is difficult for this display device to represent multiple colors, but it can only represent shades of black and white. In order to represent multiple colors, it is necessary to apply color filters to the upper portion, like in a liquid crystal display device. This leads to low reflectance and makes it hard to control the size of capsules, thus facing the problem causing difficulties in controlling the driving speed of the particles and the contrast ratio of pixels.
Korean Patent No. 2005-0055557 discloses a method of microencapsulation of a pigment as a color enhancer in the manufacture of multi-color electrophoretic particles. However, light transmittance is lowered due to increased crystallinity of the pigment particles and increased particle size. Therefore, reflectance may be reduced when pixels are displayed, and coloring power reduction may occur due to the migration of the pigment during the manufacture of the particles.
In addition, the technology disclosed in U.S. Patent No. 2009-0009852 is disadvantageous in that the process of incorporating an ionic monomer in pigment particles and the centrifugation of polymerization by-products and residual monomers in the subsequent polymerization process need to be performed repeatedly, which is cumbersome, and it is hard to adjust the degree of polymerization to achieve desired dispersion force.
Further, in Korean Laid-Open Patent No. 2010-0048076, an electrochromic layer is introduced and used as a reversible color filter layer, which is, however, not appropriate to represent a wider color area. Also, the electrowetting display disclosed in Korean Laid-Open Patent No. 2012-0021075 uses color filters and a reflective plate separately and therefore cannot achieve high reflectance and high color reproductivity because incident light is absorbed and scattered by the color filters.
Korean Laid-Open Patent No. 2010-0020105, which uses electrochromic elements as color filters for an electrophoretic display containing black and white particles to display black and other colors, is disadvantageous in that color reproductivity is low and it is difficult to represent pure colors.